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      1 /* @(#)s_logb.c 5.1 93/09/24 */
      2 /*
      3  * ====================================================
      4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
      5  *
      6  * Developed at SunPro, a Sun Microsystems, Inc. business.
      7  * Permission to use, copy, modify, and distribute this
      8  * software is freely granted, provided that this notice
      9  * is preserved.
     10  * ====================================================
     11  */
     12 
     13 #include <sys/cdefs.h>
     14 #if defined(LIBM_SCCS) && !defined(lint)
     15 __RCSID("$NetBSD: s_logb.c,v 1.12 2011/08/03 14:13:07 joerg Exp $");
     16 #endif
     17 
     18 /*
     19  * double logb(x)
     20  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
     21  * Use ilogb instead.
     22  */
     23 
     24 #include "math.h"
     25 #include "math_private.h"
     26 
     27 #ifndef __HAVE_LONG_DOUBLE
     28 __strong_alias(logbl,logb)
     29 #endif
     30 
     31 double
     32 logb(double x)
     33 {
     34 	int32_t lx,ix;
     35 	EXTRACT_WORDS(ix,lx,x);
     36 	ix &= 0x7fffffff;			/* high |x| */
     37 	if((ix|lx)==0) return -1.0/fabs(x);
     38 	if(ix>=0x7ff00000) return x*x;
     39 	if((ix>>=20)==0) 			/* IEEE 754 logb */
     40 		return -1022.0;
     41 	else
     42 		return (double) (ix-1023);
     43 }
     44